The present invention relates to a head for loading and injecting molding sand (sand and related additives) by means of compressed air, in machines for forming sand cores within dies or openable core boxes.
As is known, heads for loading molding sand for providing sand cores within openable dies generally consist of a cylindrical chamber with a vertical axis, downwardly coupled to a filling bracket or frame of a core box, and through which, entering from above, the molding sand is fed up to a preset level into said chamber. Once the level is reached, by injecting compressed air into the chamber the sand is rapidly and suddenly pushed, in practice shot, inside the core box, where it is compressed and compacted. At the end of the sand injecting and compaction operation, the core box is moved away and then opened, and the pressed core is extracted and moved away by various extraction and removal means.
It is also known that the use of compressed air for sand injecting along the cylindrical chamber and into the core boxes causes, especially in the injecting chamber, serious problems related to the systems used for the injection of the air, for the distribution thereof in the chamber and for its discharge after the injecting step. In particular, the occurring problems reside in the fact that harmful air bubbles form in the sand being fed, a vorticose air current arises, causing an insufficient density of the sand, and an irregular or uneven distribution of the density of the snad also occurs due to the position of the air discharging hole or holes after injecting.
In order to eliminate these serious disadvantages, various solutions have already been proposed, including discharging the air by means of discharge holes located and pointed towards the top of the head, as well as sending a greater amount of compressed air directed axially into the injecting chamber and a smaller amount thereof directed, instead, radially with respect to said chamber, through holes provided at its end.
Even these solutions, though they have improved the injecting operation and the quality of the molded cores, in practice have not completely solved the problem of the formation of air bubbles and of the regular compaction of the sand.